Automatic vicat control of mold



May 30, 1950 R. J. MILLER 2,509,692

AUTOMATIC VICAT CONTROL OF MOLD EXTRACTION Filed Sept. 14, l945 3 Sheets-Sheet l WHY/11ml J lNVENTO R ATTORN EY y 1950 R. J. MILLER 2,509,692

AUTOMATIC VICAT CONTROL OF MOLD EXTRACTION Filed Sept. 14, 1945 3 Sheets-Sheet 2 EXPANSION/PERCENT} INVENTOR TgzzmydJYVM/f ATTORN EY May 30, 1950 R. J. MILLER AUTOMATIC VICAT CONTROL OF MOLD EXTRACTION 5 Sheets-Sheet 5 F'i'led Sept. 14, 1945 INVENTOR A FaynmydfJW/Y/GV ATTORNEY Patented May 30, 1950 TA'TE'iS PATENT OFFICE .A,UT MATIC VICAT CONTROL OF MOLD EXTRACTION 38 Claims.

" This invention relates to the testing of materials todetermine: when-asubstance has attained plastic substance such' as gypsum, plaster of 1.,Pa1iS,:etc::possessing the characteristic of undergoing .a chemical-and physical reaction when mixedtwith water or other suitableliquid is applied to a pattern'or to-a mold'to form an investment having a casting cavity conforming .withthe'contonr of the-pattern or mold. -Many jfactors influence the setting time of mold in- .vestments; suchas variations in humidity, and "different storage ,andhandlin conditions. Suc- .,cessivetbatches of mold'investments vary some- "whatfin chemical content and introduce erratic changes inithe setting time.

After a-mold-"form-ingsubstanceof this type is -mixed with -a'suitable liquid, a chemical and 'physical"reaction takes place, "and after a substantially "predetermined time interval for any particular batch;-a-crystalline structure will begin to form, and the propagation of the crystalline structure Will-progress throughout the mass -of-the casting investment. The mold investment undergoes a preliminary-shrinkage 0r contraction cycle followed by-anexpansioncycle as the mold "investment assumes a-set, and'in certain types of 11nold-investmentsa-later contraction cycle i encounteredasa-final set is attained.

I have found that a casting investment possesses sufiicient strength that it can beseparated from a pattern or mold after *it has :passed "through its-initial contraction cycle, and that there "is a definite relation between the subsequent shrinkage and-expansion cycles and the resi'stance of the mold investment to penetration. A-mold I investment -can be most easily separated "from a pattern or mold when :it has returned to normal after completion-ofthe contraction cycle andbefore the expansion cycle-has progressed to -a point to increase thevolvmeof the mold investment. At 'that time there-are no binding *forcesbetween-the contacting surfaces of the investment and the patterniormold.

"By. :'determiningithe' resistance of -a castin investmentto'penetratiomat the time it passes through the no shrinkage or expansion point on thesubsequent shrinkageand expansion cycles, I

am able to establish .a constant factor for any class of mold investment. I can therefore ex- 5 tractgtucasting investment irom'a pattern or mold cwhen .a predetermined degree of hardness or set ihasbeenattained with assurance that the mold investment will be atyapproximately its normal fipcint of no shrinkage and expansion whereupon the investment may be'separated from the pattern or mold easier than at anyother time.

.;By checking the: resistance to penetration of a test sample of the substance used to make any casting investment, I am able to determine the time the casting investment passes through its neutral point between its shrinkage and expansionphases.

An object of this invention is therefore to pro- .vide a testin device to determine when a substance has developed .a predetermined degree of hardness or set.

Another object is to provide a mechanism for indicating when a predetermined point of shrinkage or expansion has been attained in a substancethat passes through shrinkage or expansion phases as ithardensor solidifies.

Afurther object of the invention resides in the development ofan improved 'method of determining when a casting investment should be sep- "arated from a pattern or mold to insure separation at a point when nobinding forces are encountered, to minimize breakage.

"Yet a further objectof the invention resides in the provision of a device for successively checking the resistance of a casting investment topenetration to determine" the time when the pastinginvestment may be separated from a pat- -ternor-mold-with least danger of encountering "breakage.

*Stillanother object of the invention is'to provide atestingdeviceto initiate operations of a mechanicalmechanism to perform some opera- "ticnon asubstance upon the attainment of a predetermineddegree of hardness or solidification of the substance.

Anothermbject of the invention is to provide -a-methodof and apparatus ier-separating a casting-investment froma pattern or mold wherein extraction will :be automatically efiected at a predetermined time relative to the setting of the casting investment,

"Aiurther-object (if-the invention is to provide apparatus controlled by the degree of hardness --oithe-mcldingmaterialicr extracting the casting --investment.

A further object of the invention is to provide apparatus for measuring the hardness of the molding material at predetermined intervals and at spaced points, and operative upon the development of a predetermined degree of hardness in the molding material to set in motion other automatic apparatus for separating a mold from a contour former or pattern.

Yet a further object of the invention is to provide a method and apparatus wherein a sample of a molding material is segregated and tested for its physical qualities, and the treatment of the mold is controlled by the physical qualities developed in the sample.

Another object of the invention is to provide an apparatus wherein a freshly mixed batch of a hydrosetting plastic casting investment such as gypsum is separated into two parts, one part being introduced into a flask to form a mold and the other part being segregated and continuously tested for change in hardness, the casting investment being extracted from a pattern or mold when the sec-- ond part has been found to have a predetermined degree of hardness.

A further object of the invention is to provide apparatus of the type described, which shall be of improved design and easily manufactured and maintained in operation.

Other objects and advantages of this invention will be apparent from the following detailed description considered in connection with the accompanying drawings, submitted for purposes of illustration only, and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims.

In the drawings wherein similar reference characters refer to similar parts throughout the several views:

Fig. 1 is a side elevation, partly in section, of a device embodying the invention.

Fig. 2 is a sectional View taken substantially on the line 2-2 of Fig. 1, looking in the direction of the arrows.

Fig. 3 is a horizontal sectional view taken substantially on the line s 3 of Fig. 4, looking in the direction of the arrows.

Fig. 4 is a vertical sectional view of the upper portion of the device shown in Fig. 1.

Fig. 5 is a diagram showing the relation between the testing apparatus and the mold extracting apparatus.

Fig. 6 is a graphical chart showing the variation in physical characteristics of a typical casting investment.

Before explaining in detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The testing apparatus shown in Figs. 1 to 4 comprises a base member l having a frame member l2 and a cover member 13, the three members being fitted together to constitute a housing for certain movable parts of the apparatus.

One or more vertical posts l extend between the base In and the frame member l2, to support the latter. In the lower portion of the housing is journaled a horizontal shaft I4 driven by a small electric motor it, a reduction gear [8 of 4 suitable construction being interposed between the motor l6 and the shaft to cause the shaft to rotate a slow speed.

In order further to reduce the speed of the shaft M, a cam 20 i mounted upon the shaft l4 and operates to intermittently open and close a microswitch 22 connected in the wiring of the motor in such a manner as to intermittently out oil the supply of electric current thereto and thus allow the motor to stop until an adjustable time relay again starts the motor. The time relay may be set to close the circuit to start the motor 16 at any desired time intervals as for example from five to fifteen seconds depending on the frequency it is desired to test the substance undergoing examination.

At the upper portion of the housing is provided a rotatable sleeve 24, sealed against the entry of foreign matter by means of a sealing gasket 28, held in place by a collar 21. Slidably mounted in the sleeve 21; for verticalmovement is a shaft 28 having at its upper end a tray 3|! within which is removably seated a container 32,.oi circular cross-section adapted to receive a quantity of the material 33 to be tested, for example a hydroetting plastic casting investment such as gypsum or plaster, etc.

A cam 34 is mounted on shaft I4 and contacts a spherical bearing 36 at the lower end of shaft 23, so that with each rotation of the cam the shaft 253 with its tray 30 and container 3?. will be moved upwardly by a distance equal to the eccentricity or throw of the cam.

A pin 38 is fitted in the sleeve 24 and slides in I a longitudinal groove 49 formed in the shaft 28,

to cause the shaft 28 to rotate with the sleeve 24, while permitting longitudinal movement of the shaft 28 in the sleeve 24. The arrangement conwhich engages the outer surface of portion 44,

so that'as the collar is is rotated in the clockwise direction as viewed from above, the sleeve 24 and ait 2.3 will rotate with it, but movement of the collar 46 in the opposite direction will not cause rotation of the sleeve 0r shaft.

Oscillating movement of the collar 46 is brought about by means of a cam 50 mounted on shaft I4, and adapted to engage the lower end of a rocking lever 52. The rocking lever 52 is pivoted intermediate its ends by means of a pin 5% to a vertically extending portion of the frame member til, the upper end 56 of the lever 52 being formed as a ball and engaging in an aperture in a boss 58 formed on the collar 46.

The lower end of the lever 52 is formed of hooked shape as indicated at 59, to engage the cam 59 as shown in Fig. 2. It will be seen that upon each rotation of the shaft i l the cam 50 will move the upper end 56 of the lever '52 to the left as seen in Fig. 2, causing rotation of the collar it in the clock-Wise direction as viewed from above, and producing an interrupted rotation of the container 32 and its contents.

After the cam 50 has passed the end 59, the rocking lever will be returned, by spring means (not'shown), to its original position, and upon further rotation of the shaft M the cycle just described will be repeated.

In orderto permit the stroke of the end 56 of the lever 52 to bevaried, additional holes 55 and fer terate-reception er pin} 54 are Fprovided in the housing I2 and in the rocking never 52 respectively. p The housingl' l2, l3 'is'formedin the hollow :shaipe show-n, sc' as to constitute" a container for lubri ant, which will be distributed bythe cams "as and'fit to other moving portions 'of-theappalation; apair of horizontal ways I4. so-that rotation of gear 62 will cause the plate 72 to recipro- "catein-the ways "I I. The waysl I-"are secured to the upper portion of member'ISby means of bolts '55, and one of the ways maybemade -adjustable by means of bolts I8 and shims 80.

The plate IZis formedwith an annular flange 32 which extends upwardly through anaperture 8% in the cover member I3 and supports a column 85. In order'to prevent the entry of foreign matter through the aperture 84, a flexible sealing gaskettl is secured by screw/s38 to the flange 82 and to the member I3.

The columnfifi carries'a'control head 90,- which is adiustably mounted thereon. The head 86 maybe formed in two sections, secured together by means of bolts Carried by the head 98 in juxtapositionto the cOntainerSZ isa Vicat needle92, designed to test'the resistance to penetration of the material 33 in -the "container.

Needles92 of different sizes may be selectively mounted 'in' a cylindrical "holder "9'4, provided at its upper end with a pin 96 whereby weights 98 maybe placed upon the holder to add to the weight thereof "and thereby increase the force urging the needle'M downwardly. 'The'holder M ismounted by means 'of upper and lower cross pieces and ilit hetween two'fle hie ribbons Hi2 passingcver pulleys I04 'and H mounted on's hafts 'iiiii'and IEI'I in the testinghea-d '98. One end or the ribbons-I92 are secured to the upper cross pieces I69 by'meansof pins, and the other ends of the ribbons pass through the lower cross pieces 'IBI which act as guides and aresecured to cneend of'fsprings' Hi3 having their upper ends secured'tothe'upper cross pieces I08 as illustrated. The ribbons I02 thus resiliently the pulleys I-Ihi' ahd I65.

Theshafts IE6 and fill are mounted in adjustable'bearings I 39, which if desired may be of peweled or other low friction type-to minimize resistanceto rotation of the pulleys. Rotation of pulleys Ed t in either "direction is limited by means of a pin lit mounted in a lateral wall of the testing head and extending into'an arcuate slot 'lil formed in one of the "pulleys 'IM as illustrated.

A magnet I I2 is mounted on the ribbons I02 by "by'means of's'crews I22 seated invertic'al slots I24, adjustment being brought about by 'i'neans beneath the bracketIZB. The "upper end of the screw I26 engages a horizonta'lflange I35 formed *onbracket IZE, so that by loosening 'screws- I22 and operatingscr'ew l26'the capsule II6 may be brought to the desired position.

'Within the capsule I lfi ismounte'd a swinging switch member I32, pivoted at 134 andformd with two depending arms. Upon one of the depending arms is mounted an armature I36, of

form-magnetic material; so" that when the magnet I I2 moves to the level of the armature I36,

the armature will be attracted'to the magnet and will rotate'the switch member I32 in the clockwise direction about its pivot I34 as viewed in 'FigJl. I I

The switch member I32 is formed with a'sec- 0nd depending arm I38, of electrically conducting material adapted to move into and out of contact with a drop or mass M8 of mercury or other electrically conductive material. The arm I38 and mercury I iB'constitute a switch to con.- trol a circuit I 2, inthe'knownmanner, so that when the armature 535 is moved in the clockwise direction as above described the circuit will be closed.

"As illustrated diagrammatically in'Fig. 5,-the circuit I42 controlled by movem'ent'of the'Vicat needle 92contrcls a relay switch I43 of a second circuit Hit. The second circuit It? communicates with a suitable source of current and is connected to energize a solenoid N35 to open a valve l it when the solenoid is energized. The valve H38 is'positioned in a conduit I48 interposed between a source I 58 of fluid subjected to pressure and a cylinder I52 having a piston I54 slidahly mounted therein.

Closing of the switch Ilia-Mil by movement of-the Vicat needle '92 will result in upward movement of the piston'IEt in the cylinder I52 as illustrated in- Fig. 5. The piston I'M is connected through a pistonrod I55-and other mechanical means indicated diagrammatically at I55 to afiask I58 such asthe cope portion-cf a mold in such manner that upward movement of the piston IM will result in extraction of the cope mold I59 from a contoured member or pattern ISI.

In'addition to the adj ustments above described, the entire-head 98 may be adjusted verticallyof the column ihe head ihi is siidahle on the column by virtue of a circular b'e'aring'member I62. The upper portion "of the column 86 is 'formed with a vertical'groove It I'to "receive a raclz I66 secured therein by means of screws 161. A pinion I68 is jcurnalled in the head on a transverse shaft l 'lil a nd engages the rack ISB so that rotation of the pinion will move the head up or downalong the column 86. One or more hand levers or cranks II2 are fixed to the shaft iii! to permit such rotation.

-In order to facilitate the "vertical adjustment or thehead 9G, a counterweight I'M is'suspended at the end of the headti! by means of a cable 5%. The cable H6 passes over a pulley I'IB mounted on the of the head 98; and a second pulley I89 mounted in the upper end; of the column 3S and the opposite end of the cable is attached to a bracket I32 fixed te -the upper end of the head. In-this way, the counterweight I'M substantially balances the"'weight of the head,

so that adjustment'ofthe'latter'is facilitated.

The diagram of Fig. dillustrates the progressive change of physical characteristics of a typical casting investment of the hydro-setting type such for example as gypsum, plaster of Paris, etc. after having been mixed with water or other suitable liquid. The curve marked A is the shrinkage and expansion curve while the curve marked B indicates the crushing strength of the mold investment in pounds per square inch, or its resistance to penetration.

- The casting investment is preferably introduced into the liquid with which it is to be mixed at the point E 8!] on the chart, and is allowed to soak therein for any suitable predetermined interval of time depending on the type of mold investment employed, such for example as for one minute or to the point 592 on the chart. The casting investment is then mixed for a suitable predetermined interval of time depending on the materials employed, such for example as for one 'minute or from the point I92 to the point I94 on the chart.

After the mixing operation has been performed, the casting investment in the form of a slurry is introduced into the flask I68 having a pattern lfil therein. A sample batch of the mix is poured into the container 32 and is positioned on the tray 30 of the testing device. A setting or hardening action occurs after a substantially predetermined time interval depending on the type of casting investment employed due to a combined chemical and physical reaction that takes place after the mixing of the casting investment forming ingredients.

Certain types of casting investments pass through a creaming phase as illustrated between the points I94 and 95 on the chart, and thereafter a crystalline structure will begin to form and will propagate throughout the mix as the investment attains a set or hardens. The setting action is generally accompanied by an initial contraction or shrinkage as the mold forming investment begins to solidify or set such for example as from the point M to the point I98 on the chart due to a contraction of the slurry. Thereafter,

the mold passes through an expansion cycle, returning to the normal after completion of the shrinkage cycle and before the expansion cycle has progressed to a point to increase the volume of the investment as illustrated at 268 on the chart, and continues to expand to a point such as 202 due to an expansion of the slurry as crystallization or solidification progresses iroughout the mold forming investment.

The curve B indicates the progressive increase of the crushing strength of the investment or its resistance to penetration as it passes through its successive shrinkage and expansion cycles. The investment has no resistance against crushing unti1 the point 263 is reached corresponding with the beginning of the formation of the crystalline structure as illustrated by the point I96 on the curve marked A. It thus appears that in the example illustrated, the mold has no appreciable resistance to crushing or penetration until approximately eight minutes after the investment is introduced into the liquid.

In the illustrated example the crushing strength or resistance to penetration increases substantially as a straight line function from the point 210 corresponding with the point on the A scale indicating substantially no contraction or expansion. The casting investment possesses sufficient strength that it will hold together and can be extracted from a pattern or mold some- -what before it reaches its point of maximum shrinkage indicated by the point I98 on the A scale.

As pointed out above, it is desirable that the investment be extracted from the pattern or mold at substantially the no shrinkage and expansion point so that the minimum binding forces will be encountered between the casting investment and the pattern or mold. The test sample 33 in the container 32 exhibits the same physical characteristics as the casting investment introduced into the flask Hi3 because they are both taken from the same mix.

As indicated by the chart, there is a definite relation between the shrinkage and expansion cycles of the casting investment and its crushing strength or resistance to penetration. By suitably calibrating the Vicat needle 92 by removing or adding weights 98 on the holder 94, and using a Vicat needle $2 of appropriate size the testing device can be calibrated for any particular casting investment.

By checking samples of casting investments of various classes I have been able to determine a relation between the resistance to penetration and the shrinkage and expansion cycles of each class of investment. With this information known, the control testing device is so calibrated that the Vicat needle 92 will be moved upwardly by the increasing resistance to penetration when the setting or hardening of the test sample 33 has progressed to the desired point on the successive shrinkage and expansion cycles illustrated on the curve A of Fig. 6.

Operation of the testing devic is started by actuating a switch controlling the motor l6 whereupon the shaft 94 is rotated at slow speed. Rotation of the shaft it is operable through the cam 34 to elevate the shaft 28 to project the Vicat needle 92 into the test sample 33.

As illustrated in Fig. 2 the cam 34 operates .to elevate the shaft 28 and container 32 during approximately one-half of the revolution of the shaft it. When the shaft 28 and container 32 are in the lowered position with the Vicat needle 52 out of the test sample 33, the cam 55} engages the hooked end 59 of the lever 52 to move it angularly about the pin 54. When the lever 52 is thus actuated its upper end 56 oscillates the boss 58 and collar 46 in the clock-wise direction as viewed from above Fig. 1 whereupon the one-Way clutch 48 rotates the sleeve 24 in the housing. The shaft 28 operably connected to the sleeve 24 by the pin 38 sliding in groove in will be rotated with the sleeve 24 to index the container 32; It thus appears that as the shaft I4 is rotated through one complete revolution to elevate the shaft 28, the container 32 will be indexed so that the Vicat needle 92 will be projected into a different portion of the test sample 33.

Progressive oscillation of the sleeve 24, by actuation of the lever 52 and collar 46, is effective through the gear 52 to rotate the gear 62 carried by the stud 6!! secured in the cover plate [3 of the housing. Rotation of the gear 62 is eifective through cam 64, strap 86 and link 68 and pin iii to reciprocate the base plate 12 in the ways "M to move the head 9i) toward and away from the shaft 23 to project the needle 92 into a fresh portion of the test sample 33 after the container 32 has been rotated a complete revolution.

It will be apparent that the needle 92 is moved back and forth from a point adjacent the outer 33 to penetration. of'the needle 92 progressively increases asfindic'ated by the scale B of Fig. 6,. When the resistance to penetration reaches a point'that the needle 92 will not project into the. test specimen 33, the Vicat needle 92' and the holder 94 will be elevated, whereupon the flexible ribbons I02 rotate the pulleys Ibfil and 5 535. in the clock-wise direction as viewed in Fig.

When the test specimen 3% attains a sufficient set that the Vicat needle is elevated to such a point that the magnet Ht carried by the ribbons N32 is moved downwardly in alignment with the armature I36 of the sealed capsule or tube M5, the armature I36 is attracted by the maget H3 whereupon the switch member I32 is oscillated about its'pivot led to move the arm I38 to contact the drop of mercury or other electricall conductive material I511 to; close the circuit through the leads I42.

Closing of the circuit I42 is operable through the relay switch, I43 to complete a circuit through the leads Ifidto energize thesolenoid M5 to open the valve Hi5 positioned in the conduit I43. Opening of the valve M6 in the passage I55 directs fluid under pressure from the source of fluid pressure 150,120 thecylinder I52 to elevate the piston I54. Elevation of the piston Inn is operable through the piston rod I55 and mechanism E56 to extract the mold I55 from the pattern IEI.

The actuating mechanism iscalibrated in such a manner that extraction of the casting investment from the pattern or mold will occur at substantially the point of no shrinkage or expansion indicated by the point 200 on scale A of the chart Fi 6 because at that time no binding forces will be encountered between the casting investment and the surfaces of the pattern or mold.

By checking the successive shrinkage and expansion cycles of a particular casting investment, the point of maximum shrinkage I35 and the point of no shrinkage and expansion 200 on the expansion cycle, and the point 282 of maximum expansion can readily be determined. By calibrating the testing device in such a manner that the magnet H2 actuates the switch I32 by attracting the armature I36, and suitably calibrating the relay I43 it is possible to assure actuation of the mold extracting mechanism at the precise time that the mold investment is passing through its no shrinkage and expansion point on the curve illustrated in Fig. 6. Minimum mold breakage will thus be encountered, and molds can successively be extracted with assurance that they will be subjected to minimum binding forces.

While this invention has been described with particular reference to casting investments it will apparent that it is equally applicable to the testing of any substance that undergoes a change whereby the resistance of the substance to penetration is increased or decreased. It will also be apparent that mechanism capable of performing any desired operation or sequence of operations can be set in motion and actuated automatically depending on the increase in hardness or solidi fication of the substance being tested. If desired the device can be calibrated to set any progressively rotated. each time it is elevated to project the needle. 9.2.

mechanism. in motion. upon the attainment or any desired degree of shrinkage or expansion calibrating the device to actuate a switchupon. the attainment of predetermined resistance to penetration.

Features disclosed but not claimed herein are point of no expansion contraction, forming a mold of an investment mix embodying substantially the samepred ned proportions of water plaster of Paris i separating the mold from the pattern whena resistance to penetration encountered in. said. mold, mix corresponding withthe resistance to penetration at the point of no expansion and contraction of saidfirst mentioned mix.

2. The method of forming a mold and extracting it from a pattern and flask which comprises g forming an investment mix embodying substan tially predetermined. proportions of a batch of plaster of Paris water, testing this mix to determine its hardness at its point of. no expansion and contraction, forming a moldof a, second mix formed of substantially the same predetermined proportions of water and plaster of-, Paris from said batch, and separating the mold; from the pattern and flask when its hardness progresses to a point substantially the same as the; hardness of the first mentioned mix at its point of no expansion and contraction.

The method of forming a plaster oi.l?aris mold and extracting it from a pattern which comprises forming an investment mix of plaster of Paris of a class having the characteristics of undergoing an initial contraction followed by a subsequent expansion and as it hardens, testing the mix to determine its hardness at its point of no expansion and contraction, forming a mold of plaster of Paris of said class, and separating the mold from the pattern when its hardness approximates the hardness of plaster of Paris of said class at its point of no expansion and contraction.

4. The method of forming a mold of a hydrosetting plastic casting investment such as gypsum possessing the characteristic of attaining a set and extracting the mold from a pattern which comprises forming an investment mix embodying substantially predetermined proportions of a batch of gypsum and Water, testing this mix to determine its degree of set at its point of no expansion and contraction, forming a mold of a second mix formed of substantially the same predetermined proportions of water and gypsum from said batch, and separating the mold from the pattern when its degree of set progresses to a point substantially the same as the degree of set of the first mentioned mix at its point of no expansion and contraction.

5. The method of forming a mold and extracting it from a pattern which comprises forming an investment mix embodying substantially predetermined proportions of a batch of plaster of Paris and water having the characteristics of unsaid, batch, and;

dergoing an initial contraction followed by a sub- 2 sequent expansion as its setting progresses, testing this mix to determine its degree of setting at its point of no expansion and contraction, forming a mold of a second mix formed of substantially the same predetermined proportions of water and plaster of Paris from said batch, and separating the mold from the pattern when its degree of setting approximates the degree of setting of said first mentioned mix at the point of no expansion and contraction.

6. The method of forming a mold and extracting it from a pattern which comprises forming an investment mix embodying substantially predetermined proportions of a batch of plaster of Paris and water having the characteristics of un dergoing an initial contraction followed by a subsequent expansion and an increasing resistance to penetration as it attains a set, testing this mix to determine its resistance to penetration at its point of no expansion and contraction, forming a mold and a test specimen of a second mix formed of substantially the same predetermined proportions of water and plaster of Paris from said batch, and separating the mold from the pattern when a resistance to penetration is encountered in the test specimen substantially corresponding with the resistance to penetration of said first mentioned mix at its point of no expansion and contraction.

7. The method of forming a mold and extracting it from a pattern which comprises forming i an investment mix embodying substantially predetermined proportions of a batch of plaster of Paris and water, testing this mix to determine its degree of set at its point of no expansion and contraction, forming a mold and a test specimen of a second mix formed of substantially the same predetermined proportions of Water and plaster of Paris from said batch, and separating the mold from the pattern when the degree of set of the test specimen progresses to a point substantially the same as the degree of set of the first mentioned mix at its point of no expansion and contraction.

8. The method of forming a mold and extracting it from a pattern which comprises forming an investment mix embodying subsbtantially predetermined proportions of a batch of plaster of Paris and water, testing this mix to determine its hardness at its point of no expansion and contraction, forming a mold and a test specimen of a second mix formed of substantially the same predetermined proportions of Water and plaster of Paris from said batch, and separating the mold from the pattern when the hardness of the test specimen progresses to a point substantially the same as the hardness of the first mentioned mix at its point of no expansion and contraction.

RAYMOND J. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,505,724 Nichols Aug. 19, 1924 1,544,059 Dimick June 30, 1925 2,003,863 Melton June 4, 1935 2,101,677 Hagemeyer Dec. 7, 1937 2,129,043 Bortsch Sept. 6, 1938 2,156,523 Campbell May 2, 1939 2,201,037 Hagemeyer May 14, 1940 2,201,131 Jungersen May 14, 1940 2,321,717 Wallace June 15, 1943 2,333,747 Sklar Nov. 9, 1943 2,346,182 Pattison Apr. 11, 1944 OTHER REFERENCES Camp and Francis The Making, Shaping and Treating of Steel, fifth edition, page 414.

Mellor Inorganic and Theoretical Chemistry, vol. III, page 773. 

